Microencapsulation of copigmented anthocyanins using double emulsion followed by complex coacervation: Preparation, characterization and stability

Abstract

This work focused on anthocyanin-rich black rice extract (ATC) and copigmented anthocyanins (ATC-CTC) microencapsulation using double emulsion and complex coacervation with different hydrophilic emulsifiers (gelatin-acacia gum: GE-AG, chitosan-carboxymethyl cellulose: CS-CMC). Four freeze-dried microcapsule types (GE-AG/ATC, GE-AG/ATC-CTC, CS-CMC/ATC, and CS-CMC/ATC-CTC) were prepared. Morphology, microencapsulation yield, and physical and chemical properties were investigated. Complex coacervated double emulsions prepared with GE-AG and CS-CMC were morphologically representative of multiple and single cores, respectively. GE-AG/ATC-CTC had the most desirable chemical properties with high anthocyanin content (0.76 g/100 g dw) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS•+) scavenging activity (5.8 μg Trolox/100 g dw). Fourier transform infrared spectroscopy confirmed the hydrophilic emulsifier's electrostatic interactions between protonated amines and carboxylate. X-ray diffraction spectra of all microcapsules indicated their amorphous structure. During storage, CS-CMC/ATC-CTC had the highest anthocyanin stability, the lowest reaction rate constant (4.8 × 10−3 day−1), and the highest values for half-life (150 days), decimal reduction time (497 days), thermal resistance temperature (78.1 °C), as well as the lowest activation energy (23.7 kJ/mol). According to the thermodynamic properties, the copigmentation contributed to lower negative entropy (ΔS), and the enthalpy (ΔH), and Gibb's free energy (ΔG) suggested that the microencapsulated anthocyanin degradation reaction was endothermic and spontaneous.